1. Field of the Invention
The preferred embodiments of the present invention relate in general to a device which prevents mirror recoil. More specifically, the preferred embodiments of the present invention relate to a device which prevents mirror recoil in a photographic device such as a camera when a quick return type mirror is lowered.
2. Description of the Related Art
FIG. 11 is a cross sectional diagram of a conventional single lens reflex camera. A light ray 102, entering from a lens 101 mounted in a camera body 100, is reflected upward by a main mirror 1, and is guided to an eyepiece lens 104. The main mirror 1 has a semi-transparent portion, and a portion 102a of the light ray 102 passes through the semi-transparent portion of the main mirror, is reflected by a sub-mirror 2 and guided to a rangefinding element 103 in a lower portion of the camera body.
The main mirror 1 is fixed in a main mirror support frame 202. The main mirror support frame 202 has a hole 205 and is rotatably, axially supported with a rotary shaft fixed to the camera body 100. A shaft 206 and pins 207 and 208 are fixed to the main mirror support frame 202.
A pin 219 is fixed to the camera body 100. The pin 219 can engage with a U-shaped groove of the sub-mirror support frame 212. However, the pin 219 does not engage with the U-shaped groove of the sub-mirror support frame 212 in the position shown in FIG. 11. Eccentric pins 220 and 222 are mounted, and are capable of rotary adjustment, in the camera body 100. The sub-mirror 2 is fixed in a sub-mirror support frame 212. The sub-mirror support frame 212 is axially supported and rotatable around a shaft 206. A pin 215 is fixed to the sub-mirror support frame 212. A toggle spring 216 is suspended between pins 215 and 207 to urge the sub-mirror support frame 212 toward the eccentric pin 220. A mirror return spring 230 is suspended on the pin 208 and a pin 209 fixed to the camera 100 body, and urges the main mirror support frame 202 toward the eccentric pin 222.
Next, the operation of a conventional mirror return device will be described. When an exposure is completed by a well known method, the main mirror support frame 202 moves counter-clockwise around the hole 205 by the action of the mirror return spring 230. The main mirror support frame 202 thus returns to the position shown in FIG. 11. Then the sub-mirror support frame 212 and the eccentric pin 220 collide, and the main mirror support frame 202 and the eccentric pin 222 collide.
In the conventional device, when the sub-mirror support frame 212 and the eccentric pin 220 collide, the sub-mirror support frame 212 recoils in a counter-clockwise direction due to the impact. This recoil alters the direction and path length of portion 102a of light ray 102 travelling toward the rangefinder element 103. Thus, during recoil of the sub-mirror support frame 212, accurate rangefinding is not performed. Accurate rangefinding must be delayed until after cessation of the recoil. In autofocus mode, during tracking of a subject in continuous photography, the delay limits the number of photographs per unit time.